Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $130.45   3.798%   $135.4045   $135.40   $135.40   $135.40  
  Purchase #2 $57.93   9.320%   $63.3291   $63.33   $63.35   $63.30  
  Purchase #3 $7.34   4.839%   $7.6952   $7.70   $7.70   $7.70  
  Purchase #4 $139.26   6.747%   $148.6559   $148.66   $148.65   $148.70  
  Purchase #5 $97.31   6.377%   $103.5155   $103.52   $103.50   $103.50  
  Purchase #6 $216.42   12.406%   $243.2691   $243.27   $243.25   $243.30  
  Purchase #7 $144.62   3.513%   $149.7005   $149.70   $149.70   $149.70  
  7 purchase totals = $793.33       $851.5698   $851.58   $851.55   $851.60